1. Field of the Invention
This invention relates generally to an interface and switch for a high speed network, and more particularly to an interface and network switch capable of communicating at a nominal rate of up to 1 gigabit per second.
2. Description of the Related Art
Interconnections of and communications among computers, peripheral devices, Internet appliances (generally referred to as network clients hereinbelow) via computer networks are ubiquitous. Moreover as applications such as, multimedia, require higher data transfer rates there is a need for more robust and faster networks.
Network switches facilitate interconnections and communications among networks and network clients. Conventional networks may utilize twisted pair cable such as Category 5 and operate at a data rate of either 10 megabits per second which generally complies with IEEE Standard 802.3, section 14, commonly known as 10 BASE-T, and 100 megabits per second which generally complies with IEEE Standard 802.3, sections 24 and 25, commonly known as 100 BASE-TX, the contents of each of which are incorporated herein by reference. As the demand for increased data transfer rates is required, a newer networking standard has been proposed that utilizes twisted pair cable and operates at a nominal data transfer rate of 1 gigabit per second (1000 megabits per second). The 1 gigabit per second transfer rate complies with IEEE Standard 802.3, section 40, commonly known as 1000 BASE-T, the contents of which are incorporated herein by reference.
FIG. 1 is schematic diagram of a typical networking system. As shown therein, a computer 10 is connected to a first port of switch 20 via a communications channel, such as, twisted pair cable 30. Switch 20 may comprise 24 ports, to allow computer 10 to communicate with other computers, peripherals, network appliances and other networks.
Computer 10 comprises a media access controller or MAC 12 and physical layer interface (PHY) or transceiver 16, which are connected to each other by an interface defined by, for example, the Media Independent Interface (MIT) for 10 BASE-T standard and for 100 BASE-TX standard or the Gigabit Media Independent Interface (GMII) for 1000 BASE-T standard. MII for 10 BASE-T standard and for 100 BASE-TX standard are discussed at IEEE standard 802.3 section 22, the contents of which are incorporated herein by reference. The Gigabit Media Independent Interface (GMII) is defined by IEEE 802.3 section 35, the contents of which are incorporated herein by reference.
Media access controller 12 controls media access of transmitting and receiving packets to and from computer 10. Typically for gigabit level products, MAC 12 and PHY 16 are implemented as individual integrated circuits.
Switch 20 comprises MAC 22n and PHY 26n, which are respectively connected to each other in accordance with an interface as defined above. MAC 22n and PHY 26n are functionally similar to MAC 12 and PHY 16 of computer 10.
When the network is operated in accordance with 10 BASE-T or 100 BASE-TX the interface is defined in accordance with Media Independent Interface (MII). The MII passes data to and from the MAC 22n in 4 bit wide nibbles. The nibbles are converted to and from 10BASE-T or 100BASE-TX on the network side. When the network is operated at a higher transmission rate in accordance with 1000 BASE-T, the interface is defined by the GMII. In accordance with GMII, data is passed to and from the MAC 22n in 8 bit wide bytes. The bytes are converted to and from 1000BASE-T on the network side. Note that if fiber is used on the network side then the bytes are converted to and from 1000BASE-X on the network side. In other words, the MII/GMII provides a standard interface from a MAC to a transceiver regardless of the actual protocol used on the network side.
In a system that complies with 10 BASE-T, the MII requires 16 connection lines or pins connecting the integrated circuit embodying PHY 16 and PHY 26 to integrated circuit embodying MAC 12 and MAC 22, respectively. Similarly, in a system that complies with 100 BASE-TX 16 connection lines or pins are required. In a system that complies with 1000 BASE-T 24 connection lines or pins are required. The number of pins required for MAC 12 is not a problem because there is only one MAC and one PHY. On the other hand since there are n ports in switch 20, and since the n MAC 221-22n are typically fabricated as a single integrated circuit 22, the number of pins are 24×n. For example if there are 24 ports then the n MAC 22 requires 24×24 or 576 pins. The higher number of pins result in a larger die, a larger package, a more complicated integrated circuit and higher costs, particularly at the higher data transfer rates.
Various attempts have been made to solve the above-mentioned problems. Two ad hoc standards, namely Reduced Media Independent Interface (RMII) and Serial Media Independent Interface (SMII) reduce the number of pins by serialization techniques for 10 BASE-T and 100 BASE-TX. The RMII technique requires 7 pins per port and the frequency doubles from 25 MHz to 50 MHz. Thus for a 24 port switch 7×24 or 168 pins are required. The SMII technique requires 2 pins per port plus 1 synchronizing pin and the frequency increases 5 fold from 25 MHz to 125 MHz. In this technique 2×24+1 or 49 pins are required for the SMII technique. As will be appreciated by one of ordinary skill in the art, these techniques operate at frequencies in which clock recovery between PHY 26 and MAC 22 is not required.
The GMII interface consists of 24 pins operating at 125 Megabits per second. However, design of such circuit is difficult as the length of the traces and impedances between the traces must match for good signal integrity at this higher frequency. This results in a more costly and complicated integrated circuit.
An additional requirement of a network circuit operating at 1 gigabit per second is to be backward compatible with 10 BASE-T and 100 BASE-TX networks. That is, the network circuit must detect the maximum data transmission rate capability and set the transmission rate to that rate. For example, if computer 10 is capable of a maximum transmission rate of 100 Mb per second, switch 20 having a capability of 1 gigabit per second, must detect the 100 Mb per second rate and set the transmission rate of the port of switch 20 connect to computer 10 to 100 Mb per second. This feature is commonly known as auto-negotiation. The auto-negotiation feature is typically implemented in PHY 16 and PHY 26n. PHY 16 communicates the auto-negotiated data transmission rate to MAC 12 and PHY 26n communicates the auto-negotiated data transmission rate to MAC 22n.
Traditional techniques either requires higher pin counts and complicated board routing.